Background removal apparatus

ABSTRACT

Improved background removal apparatus includes a magnetic brush for removing background toner from the photoreceptor of an electrostatic reproduction machine, and a reclaim roller for removing the toner from the magnetic brush. The background removal apparatus is neatly integrated into the developer of the machine so as to form a developer/background removal apparatus unit. The reclaim roller is positioned so as to both dispense the reclaimed toner back into the main sump of the developer, and to serve as a &#39;&#39;&#39;&#39;doctor blade&#39;&#39;&#39;&#39; for the magnetic brush. To promote mixing and increase carrier life, the magnets within the magnetic brush are arranged so as to allow the carrier beads of the brush to fall freely into the sump of the background removal apparatus after sweeping the photoreceptor surface. To provide for easy maintenance, the background removal apparatus includes an opening in the top thereof for loading carrier into the apparatus, and an opening in the bottom thereof for unloading the carrier into the main sump of the developer.

United States Patent 1191 Dennie et al.

[ Nov. 18, 1975 BACKGROUND REMOVAL APPARATUS [75] Inventors: Richard H. Dennie, Walworth;

Michael R. Stanley, Pittsford, both of NY. 1

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Sept. 25, 1974 [21] Appl. No.: 508,953

Primary Examiner-Robert P. Greiner Attorney, Agent, or Firm-James J. Ralabate; Bernard A. Chiama; Earl T. Reichert [57] ABSTRACT Improved background removal apparatus includes a magnetic brush for removing background toner from the photoreceptor of an electrostatic reproduction machine, and a reclaim roller for removing the toner from the magnetic brush. The background removal apparatus is neatly integrated into the developer of the machine so as to form a developer/background removal apparatus unit. The reclaim roller is positioned so as to both dispense the reclaimed toner back into the main sump of the developer, and to serve as a doctor blade for the magnetic brush. To promote mixing and increase carrier life, the magnets within the magnetic brush are arranged so as to allow the carrier beads of the brush to fall freely into the sump of the background removal apparatus after sweeping the photoreceptor surface. To provide for easy maintenance, the background removal apparatus includes an opening in the top thereof for loading carrier into the apparatus, and an opening in the bottom thereof for unloading the carrier into the main sump of the developer.

6 Claims, 5 Drawing Figures Sheet 1 of 3 U, S. Patent Nov. 18, 1975 U.S. Patent Nov. 18, 1975 Sheet 2 of3 3,920,329

FIG. 3

I I l +500 -5OO O CHARGE BAR BIAS (VOLTS) BACKGROUND REMOVAL APPARATUS BACKGROUND OF THE INVENTION Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material afiixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surbeing reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic icharge pattern or latent electrostatic image in conformity with the configuration of the original pattern.

The latent electrostatic image is developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited, and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the image of the original being produced. The powder image is subsequently transferred to a sheet of paper or other transfer member, and suitably affixed thereto to form a permanent The latest concept for electrostatic reproduction machines utilizes high speed flash exposure of a document, and a moving photoconductive material in the form of an endless belt which is continuously charged.

Additionally, such reproduction machines are provided with a developing system which supplies toner particles in relatively large quantities for solid area coverage, such as a magnetic brush developing apparatus. Thus, after the belt passes the magnetic brush assembly for example, a xerographic powder image is formed on the beltwhichcorresponds to the electrostatic latent image. This powder image is then transferred to a support surface (e.g., a sheet of paper) to which it is fused by a fusing assembly whereby the powder image is caused to adhere to the support surface permanently.

The latest electrostatic reproduction machines are stantially in excess of any previous electrostatic reproduction machines, and are intended to compete with other types of printing machines, e.g., offset printing machines. Because of this, it is desired that the quality of the copies made, be extremely high. Important to high quality copies is the removal of all or substantially all of the background particles (i.e., toner in non-image areas) from the photoreceptor before transfer of the developed image to a support member. As stated above, large amounts of toner are used in these high speed electrostatic reproduction machines to develop the latent electrostatic image, and to produce high quality copies, a very efficient background removal apparatus is necessary to remove any background particles which may be present after development. This apparatus must be superior to previous means used to reduce the background (e.g., lamps or pre-transfer coface, and then exposed to a light pattern of the image 2 rona charging devices used to prevent or reduce transfer of background particles) on copies in that it must eliminate all or substantially all of the background from the copies; the apparatus must also not detrimentally affect the developed image on the photoreceptor to any great degree as did some of the previous means.

It is also highly desirable that the life of the developer (carrier plus toner) be extended, and the life of the developer is directly related to background, the less the background, the longer the life of the developer. By efficiently removing all or substantially all of the background, developer life will be substantially increased, possibly doubled or even quadrupled. Also, this apparatus should be integrated into a machine so as to occupy minimal space, and cooperate with other elements of the machine, be accessible, and be designed for easy maintenance by the machine operator.

SUMMARY OF THE INVENTION The present invention is directed to background removal appa ".tus having a magnetic brush for contacting a photoreceptor to remove background toner particles, and at least one reclaim roller located so as both to remove the particles from the magnetic brush roller and discharge them into the main developer sump of the machine, and to serve as a doctor blade for the bristles (formed by magnetic carrier beads) of the magnetic brush roller. A grounded or properly biased charge bar is located so as to contact the bristles of the magnetic brush roller after they have been contacted by the reclaim roll, but before they contact the photo- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of an electrostatic reproduction machine embodying the principles of the invention.

FIG. 2 is an enlarged schematic view showing the developer, the background removal apparatus, and their interrelationship.

FIG. 3 is a plot of fractional decrease in background density versus charging bar bias.

high speed machines which print copies at a rate sub- FIGS. 4 and 5 are enlarged views of the background removal apparatus showing the magnetic brush roller,

- the reclaim roller, the charge bar, and a detailed view of the means for unloading the apparatus.

DETAILED DESCRIPTION OF THE INVENTION For a general understanding of an electrostatic reproduction machine in which the invention may be incorporated, reference is made to FIG. 1 in which the various system components for the machine are schemati- 3 which it may be fused by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated machine 10, an original document D to be copied is placed upon the transparent support platen P fixedly arranged in an illumination assembly generally indicated by the reference numeral 11, arranged at the left end of the machine; a platen cover (not shown) is then lowered onto the original D to cover the same. While upon the platen P, an illumination system flashes light rays upon the original thereby producing image rays corresponding to the informational areas on the original. The image rays are projected by means of an optical system for exposing the photosensitiive surface of a xerographic plate or photoreceptor in the form of a flexible photoconductive belt 12. The surface of the belt was made photosensitive by the previous step of uniformly charging the same by means of a corona generating device 13. In order to effect image processing, the belt 12 is arranged on a belt assembly generally indicated by the reference numeral 14. I

The photoconductive belt assembly 14 is slideably mounted upon two support shafts, one of which is secured to the frame of the machine, and is adapted to drive a belt 12 in the direction of the arrow at a constant rate. During this movement of the belt, the reflected light image of an original on the platen is flashed upon the surface of the belt to produce electrostatic latent images thereon at an exposure station A.

As the belt surface continues its movement, the electrostatic latent image passes through a developing station B in which there is positioned a developer/background removal assembly generally indicated by the reference numeral 15, and which provides development of the electrostatic latent image by means of a developer 16 having multiple magnetic brush 17. The developed electrostatic image then moves past a background removal apparatus 18 which removes background particles from the belt 12 prior to transfer of the developed image.

The developed electrostatic image (without background particles) is then transported by the belt to a transfer station C where a sheet of copy paper is moved between a transfer roller 19 and the belt at a speed in synchronism with the moving belt in order to effect transfer of the .developed image. There is provided at this station a sheet transport mechanism indicated generally at 20 adapted to transport sheets of paper from a paper handling mechanism generally indicated by the reference numeral 21 to the developed image on the belt at the station C.

After the developed image is transferred to the sheet, the latter is stripped from the belt 12 and conveyed into a fuser assembly indicated generally by the reference numeral 22 where the developed and transferred xerographic powder image on the sheet material is permanently affixed thereto. After each copy is thus produced, it is delivered via sheet transport mechanism 23 into an output tray 24.

Additional details regarding the subject electrostatic reproduction machine are set forth in a copending US. patent application Ser. No. 312,411 assigned to the same assignee. Although not specifically discussed herein, it is understood that the present invention may also be utilized in other types of electrostatic copying or duplicating machines, and is not limited to the high speed duplicating machine disclosed herein.

Referring to FIG. 2, an enlarged schematic view of an embodiment of the invention is shown. The latent electrostatic image is developed by a plurality of magnetic brushes 17 which move developing material (toner particles and magnetic carrier beads) up an inclined plane as shown. The developing material is then directed through a cross-mixing baffle 26, and returned to the main developer sump 28. Toner is periodically dispensed into the developer sump via a toner dispenser 30 having a porous dispensing roller 32. Further details of the developer 16 are described in US. Pat. No. 3,724,422, the disclosure of which is hereby incorporated by reference.

For purposes of illustration only, it is assumed herein that the belt 12 is initially charged to a positive polarity of approximately 900 volts or more by the corona charging device 13. After being exposed to a light pattern of the image being reproduced, the image areas are approximately 700-900 volts, but the background (non-image) areas are discharged or substantially discharged; the background areas may still have a slight positive charge of approximately 200 volts or less.

Magnetic carrier beads or particles which will place anegativecharge (via triboelectricity) on the toner particles are used in the developer 16. When the negatively charged toner is used to develop the image, the toner will be strongly attracted to the highly charged positive image areas. Some toner particles, however, may become loosely attached to the weakly charged background areas also.

The belt 12 with the developed image thereon then moves past the background removal apparatus 18 where it is contacted by the bristles of a detoned magnetic brush 36, detoned meaning that the amount of toner as compared to carrier within this apparatus is preferably less than 0.1 percent by weight. The brush 36 has a rotatably mounted cylinder 38 made out of any suitable non-magnetic material, e.g., brass, aluminum, copper, or stainless steel. Arranged within the cylinder 38 are two permanent bar magnets 40 and 42, the magnets having a magnetic strength and being arranged substantially as shown so that the bristles formed by magnetic carrier beads 44 on the periphery of the cylinder 38 are stiff enough to remove substantially all of the background toner particles from the belt 12 without substantially affecting the developed image thereon; other suitable magnet arrangements may also be used.

The bristles formed on the cylinder 38 adjacent to the belt 12 are formed by magnetic carrier beads 44 which can be coated or uncoated. It will be appreciated that bristles are formed from the outer surface of cylinder 38 due to the lines of force from magnets 40 and 42 which are oriented in polar paths as indicated by the letters N and S which illustrate north and south poles, respectively (see FIG. 5). The magnetic beads comprise any suitable material. The magnetic material may be soft i.e., retaining very little residual magnetism, or the permanent magnet type. Typical magnetic materials comprise powdered iron including types known commercially as alcoholized iron and carboxal iron, steel, nickel, alloys of magnetic iron, such asnickeliron alloys, nickel-cobalt-iron alloys, and magnetic oxides, such as, iron oxide, hematite (Fe O and magnetite (Fe O and magnetic ferritesrThe magnetic beads can be coated withan electrically insulating material. Typical coating materials are described in US. Pat. No. 2,618,551 to Walkup, US. Pat. No. 2,618,552 to Wise,

patents as well as many of the magnetic materials mentioned above, also have a triboelectric attraction for the toner particles which serves to further facilitate removal of the toner particles onto the beads.

As the bristles of the brush 36 sweep over the surface of the belt 12, background toner particles are removed by the bristles and adhere thereto. Although in absolute terms much more toner is removed from the image areas than from the background areas of the belt, percentage-wise, a much greater portion of toner is removed from the background area (approximately 80-90 percent) than from the image areas (approximately -20 percent); the image areas are not detrimentally affected. To assist in removing toner from the belt 12, the magnetic brush 36 is electrically biased to a positive polarity of approximately 150 volts (see FIG. 5). As the carrier beads leave the magnetic field of magnet 40, they fall freely into the sump 48 of the background removal apparatus. Arranging the magnets substantially as shown allows the carrier beads to fall freelly into the sump 48 rather than remain captured all the way around the cylinder 38. This improves mixing and increases the life of the carrier since each carrier bead is used less often, and the impaction rate will consequently be less. lmpaction of toner onto the carrier beads shortens the useful cleaning life of the carrier beads.

The carrier beads 44 then enter the magnetic field of the second magnet 42 and are again attracted to the cylinder 38. As the cylinder 38 continues to rotate, the carrier beads 44 pass the reclaim roller 50 which is electrically biased to a positive polarity of approximately 1,150 volts (see FIG. 5). The reclaim roller 50 serves not only to attract the negatively charged toner particles from the magnetic brush 36, but also serves as a doctor blade so as to trim excess carrier beads from the cylinder 38 which then fall back into the sump 48. The reclaim roller 50 rotates in a counter-clockwise direction as shown, and the negative toner particles 51 attracted thereto are removed by a plastic scraper blade 52 and dropped into the main sump 28 of the developer housing. It has been found that a plastic scraper blade reduces the torque requirements necessary to ro- 'tate the roller 50. An elastomeric lip seal 54 serves to prevent any of the material within the sump 48 from escaping. The reclaim roller 50 may be made of any suitable non-magnetic material, e.g., non-magnetic stain- .less steel.

To discharge any charge placed upon the carrier beads by the electrically biased reclaim roller 50, a

conductive charging bar 56 is located between the reclaim roller 50 and the belt 12. The charging bar 56 may also be made of any suitable nonmagnetic stainless steel. The charging bar 56 may either be grounded or electrically biased to a polarity opposite that of the reclaim roll (see FIG. 5). This charging bar serves to dis- .charge the carrier beads prior to the time the carrier beads reach the belt 12. It has been determined that charging bar 56 is necessary for the effective removal of background particles. Referring to FIG. 3, it can be seen that the background removal efficiency changes when the polarity of the charging bar 56 changes from positive to negative.

To make it easier for the magnetic brush 36 to remove background particles, a corona charging device 60 may be incorporated into the system as shown in FIG. 2. This corona charging device will place an appropriate charge on the background so that the background particles are more readily removed by the magnetic brush 36. In other words, by using a corona charging device 60 as shown, it can be seen that the charge on the background particles can all be made approximately the same.

Another novel feature of this invention is the arrangement of the developer 16 and the background removal apparatus 18 into a single integrated unit. When it is desired to load carrier into the background removal apparatus 18, a loading door 62 located above the magnetic brush 36 may be removed and the carrier loaded into the apparatus. This provides for easy maintenance of the apparatus. When the carrier has been spent, and it is desired to remove or unload the same from the sump 48, an unloading door 64 is provided in the bottom of the sump as can be seen more clearly in FIGS. 4 and 5. This unloading door 64 is in the form of a circular rod, one end of the door having a bent rod 66 which rides in a slotted ramp 68. When the door 64 is in its closed position a lip 70 rests upon the upper end of the slotted ramp 68. The door 64 is held in its closed position by a latch 72 on the other end thereof, the latch 72 being supported by a slot in bracket 74. When the door 64 is so latched, it is held in place against the gasket 76. Thus, it can be seen that the present arrangement provides for easy loading and unloading of the background removal apparatus 18. The overall arrangement is such that a minimum of space is occupied by the developer/ background removal apparatus 15 and a cooperative relationship is provided between the developer 16 and the background removal apparatus 18.

While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth, but is intended to cover such modifications or changes as may come within the scope of the following claims.

What is claimed is:

1. The combination of a developer having a first sump with a background removal apparatus having a second sump, the background removal apparatus being positioned above the first sump, and including (a) means for transporting magnetic carrier beads into sweeping contact with a photoreceptor to remove background toner, the transporting means including a rotatably mounted non-magnetic cylinder and magnet means positioned within the cylinder so as to permit the carrier beads to drop freely from the cylinder into the second sump after sweeping the photoreceptor and then to be reattracted to the cylinder again after being mixed within the second sump, and (b) reclaim means for reclaiming the toner from the carrier beads which are being transported into sweepingg contact with the photoreceptor.

2. The combination set forth in claim 1, and further including means for opening the second sump to allow its contents to drop into the first sump.

3. The combination set forth in claim 1, wherein the reclaim means is positioned so as to allow the reclaimed toner to be dropped into the first sumpwhen removed from the reclaim means, and further including means for removing the reclaimed toner from the reclaim means.

4. The combination set forth in claim 3, wherein the reclaim means is positioned so as to trim excess carrier beads from the transport means and drop the excess reclaim means comprises a non-magnetic roller and means for electrlcally biasing the non-magnetic roller, and wherein the removing means comprises a plast1c scraper blade. 

1. The combination of a developer having a first sump with a background removal apparatus having a second sump, the background removal apparatus being positioned above the first sump, and including (a) means for transporting magnetic carrier beads into sweeping contact with a photoreceptor to remove background toner, the transporting means including a rotatably mounted non-magnetic cylinder and magnet means positioned within the cylinder so as to permit the carrier beads to drop freely from the cylinder into the second sump after sweeping the photoreceptor and then to be reattracted to the cylinder again after being mixed within the second sump, and (b) reclaim means for reclaiming the toner from the carrier beads which are being transported into sweepingg contact with the photoreceptor.
 2. The combination set forth in claim 1, and further including means for opening the second sump to allow its contents to drop into the first sump.
 3. The combination set forth in claim 1, wherein the reclaim means is positioned so as to allow the reclaimed toner to be dropped into the first sump when removed from the reclaim means, and further including means for removing the reclaimed toner from the reclaim means.
 4. The combination set forth in claim 3, wherein the reclaim means is positioned so as to trim excess carrier beads from the transport means and drop the excess carrier beads back into the second sump.
 5. The combination set forth in claim 4, and further including means for opening the second sump to allow its contents to drop into the first sump.
 6. The combination set forth in claim 5 wherein the reclaim means comprises a non-magnetic roller and means for electrically biasing the non-magnetic roller, and wherein the removing means comprises a plastic scraper blade. 